[Infectivity of different forms of lambda bacteriophage DNA in transfection of calcinated Escherichia coli]

Infectivity of linear lambdaDNA molecules is proved to be about a hundred times higher in calcinated E. coli K12 (lambai434) than in E. coli K12(lambda-): the levels of transfection were 1-3-10(7) and 1-2-10(5) infective centers per 1 mug DNA, respectively. In E. coli JC 5743 rec B21 defective for exonucleases I and V the level of transfection was 1-3-10(6). High infectivity of linear lambdaDNA in lysogenic cells cannot be explained by a helping effect of phage particles spontaneously liberated by these cells. It can be caused by recombinations of inserted lambdaDNA molecules with prophage or by the low activity of some nucleases in the lysogenic cells. Covalently closed and "Hershey" ring forms of lambdaDNA penetrate the calcinated cells as readily as linear molecules do but the infectivity of the former ones is proved to be very low.